The poet William Blake imagined what it would be like “to see the world in a grain of sand.” Reading “Microcosm” (Pantheon, 243 pages, $25.95), Carl Zimmer’s new book on the world’s most famous bacterium, one wonders whether Blake might have phrased his reverie differently if he had had an electron microscope. Had Blake looked closely enough, at a magnification that would make sand grains look like lifeless, barren mountains, the poet would have seen a remarkably complex creature, one so beguiling that it is, as Mr. Zimmer’s title suggests, easy to imagine it as a world in miniature. The bacterium, whose genome scientists mapped fully by 1997, fights viruses, just as we do; it fights its enemies, just as we do; it even has a primitive kind of sex. It is, the author argues persuasively, a model organism, and one with much to teach our own species.

E. coli are best known as the microbes that occasionally flourish in tainted meat, and that send thousands of burger-eaters each year moaning to the nearest toilet. What is less known is that these microscopic, pill-shaped bacteria infest the guts of nearly every warm-blooded creature on earth. Within a short time after birth, a human baby contains multitudes of them — a vast colony in the lower intestine, feasting avidly on whatever she eats, from her first suck of milk to her last nursing-home pudding cup. The E. coli break down molecules of food that the human body can’t disassemble on its own, and they crowd out other bacteria less suited to cooperation with a human host (and more likely to go rogue and send us back to the toilets, or worse). Only when dangerous strains arrive and flourish — usually via a stray smear of cow feces somewhere in the butchering cycle — do the bacteria pose a threat. For the most part, E. coli are partners with humanity, having reached an uneasy evolutionary détente with us — a diplomatic pact whereby we provide food, heat, and shelter for them, and they in turn digest our food and act as our microbial proxies by conducting raids against enemy microorganisms in our intestines.

If the intra-organism dynamic is a diplomatic endeavor worthy of Henry Kissinger, the dynamic within the cell walls of a single E. coli is an engineering feat worthy of Rube Goldberg. Take their flagella — long, whip-like strands used to propel bacteria toward their food. Howard Berg, a biophysicist at Harvard, has shown that the motor that spins the flagella is powered by an intricate feat of nanotechnology: a rotary engine so small that it is literally invisible, 10 times smaller than the wavelength of visible light. The engine includes flexible couplings and gearboxes many times tinier than anything human engineering has yet accomplished. And it is just one of the intricate devices in every one of the billions and billions of E. coli in every human who has ever lived.

The intricacies of E. coli’s anatomy and relationship with neighbors make it an excellent model for understanding our own biology and behavior. Scientists mapped an E. coli genome a few years before the human genome, and they have been busy exploiting and studying it ever since, with an eye not only to figuring out what make the bacteria tick, but also to seeing whether their insights scale up to suggest ways to understand the genetics of other species. “What is true for E. coli is true for the elephant,” scientist Jacques Monod said, with a hint of hyperbole. Already, knowledge of the genetic blueprints of E. coli have made it easier to mix and match scraps of genetic material and convince the bacteria, for example, to produce human insulin.

Mr. Zimmer’s book is a mix of engagingly written accounts of scientific breakthroughs and, in parts, more personal vignettes. He opens with an account of his visit to a microbiologist at Yale, who seeds a petri dish of bacteria for him and promises it will “get stinky” as the E. coli bloom in the nutrient-rich environment of fresh agar. The visit leaves the author staring at his new bacteria farm and mooning over its potential to serve as his “lens” on life. Encounters like this, with their ecstatically reflective moments, recur throughout the narrative and are among the most memorable in the book.

There are downsides to this impressionistic approach, though. “Microcosm” will be an inhospitable environment for a reader not already acquainted with the basics of cell structure and genetics. If you don’t know a gene from a chromosome, Mr. Zimmer will not guide you by the flagellum and explain the difference, although both terms appear frequently. His prose is vivid without being misleading — surely one of the hallmarks of good science writing. When he says, for example, that the chain of sugars and peptides that make up the cell wall is “teased like threads of cotton candy,” or that the peptidoglycan layer acts as a “corset” around the cell, he is being colloquial without sacrificing accuracy.

But the impressionistic method also permits Mr. Zimmer to return frequently to the microcosmic themes — that E. coli’s habits and history mirror our own, and can contain lessons for us. These themes accomplish the other critical task of science writing: to provoke curiosity and wonder. E. coli’s adaptability is astonishing, and it rivals that of our own durable species, Homo sapiens. When cornered by foreign organisms that might try to attack an E. coli colony, for example, it employs tactics that resemble human asymmetric warfare: The threatened bacterium produces colicin, a toxin that inhibits rival strains of bacteria and kills the cells that produce it, as well as itself, thereby combining suicide bombing and chemical weaponry.

In some cases the comparison is perhaps too glib. Mr. Zimmer makes much of the stationary phase E. coli enter during periods when, having surrounded themselves with their own waste, they run out of food. Having befouled their environment and denuded it of its resources, the bacteria quit reproducing, crumple their reproductive apparatus into a compact and rugged crystalline structure, and hibernate — only to unfold and resume reproducing once lean times pass. At this, Mr. Zimmer remarks ominously, “we humans never get such a second chance.” It’s a fair shot at anti-greens, except that it’s not clear that humans won’t be able to persist through similarly difficult conditions, hunkering down while we figure out how to deal with the mess we’ve made. (Folding our genitalia into neat crystalline lattices will probably sting a bit, though.) And yet, whatever our future, we should be sure to heed the lessons of E. coli. Those little stinkers have been around a lot longer than we have, and they have some story to tell.

Mr. Wood is a staff editor at the Atlantic.